[Python-Dev] Pickle implementation questions

Bruce Christensen t-bruch at microsoft.com
Fri Jun 30 19:16:54 CEST 2006

Thanks for your responses, Martin!

Martin v. Löwis wrote:
> Bruce Christensen wrote:
> >  - Where are object.__reduce__ and object.__reduce_ex__ defined, and how
> > does copy_reg._reduce_ex fit into the picture? 
> See
> http://docs.python.org/lib/node69.html

So just to be clear, is it something like this?

class object:
    def __reduce__(self):
        return copy_reg._reduce_ex(self, -1)

    def __reduce_ex__(self, protocol):
        return copy_reg._reduce_ex(self, protocol)

Does _reduce_ex's behavior actually change depending on the specified protocol version? The only difference that I can see or think of is that an assert causes it to fail if the protocol is >= 2.

> >  - What does copy_reg.constructor() do?
> It does this:
> def constructor(object):
>     if not callable(object):
>         raise TypeError("constructors must be callable")

So it is part of the public interface? It's exported in __all__, but it appears
that it's undocumented.



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